The unanimous decision is at odds with the government's anti-cyberbullying Bill C-13, currently before the Senate.

The bill — widely panned by civil libertarians and privacy experts — would allow private telecoms to pass personal information of Canadians to law enforcement even in the absence of a warrant.

The court ruled that was unconstitutional. Police may ask for information and telecoms can, to some degree, oblige. But if that information is to be used in court, a warrant must be obtained prior to obtaining the information, the court ruled.

Open-web advocacy group OpenMedia.ca hailed the court's decision and said "the widespread practice of government authorities acquiring Canadians' private information from telecoms without a warrant must now come to an end."

The ruling is based on the case of Matthew Spencer, a young Saskatchewan man who was convicted of possessing child pornography but claimed police violated his privacy rights during their investigation.

Police suspected Spencer downloaded child pornography between August and September 2007 using the file-sharing program LimeWire.

Police said they identified the IP address Spencer used to access the child pornography, then approached his Internet service provider, Shaw Communications, for the name on the account, home address and phone number.

Police argued requesting the information from Shaw didn't constitute a search — a search would have required them to obtain a warrant — and the information Shaw provided isn't protected by privacy provisions in the Charter of Rights and Freedoms.

Spencer disagreed, and claimed he was entitled to a reasonable expectation of privacy that Shaw failed to provide.

"The issue is not whether Mr. Spencer had a legitimate privacy interest in concealing his use of the Internet for the purpose of accessing child pornography, but whether people generally have a privacy interest in subscriber information with respect to computers which they use in their home for private purposes," the ruling says.

In question period Friday, Tory MP Bob Dechert said the ruling would be reviewed and the government would "continue to protect children."

Montreal-based private investigator Claude Sarrazin said police generally feel they need more power to investigate potential crimes, not less.

"Considering the evolution of cybercriminality, officers should have a way to get personal information from Internet service providers without a warrant," he said. "When police officers are suspicious, they should be able to get who's behind an IP address."

That was echoed by the Canadian Police Association. "We're disappointed and frustrated by the ruling," CPA president Tom Stamatakis said. "It adds a larger administrative burden where we are already struggling with the burden we have."

A spokesman for Shaw Communications said the company is studying the decision, but had no further comment.

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